1. Field of the Invention
The invention relates to apparatus for producing and dispensing extinguishing fluids mixed with adjuvants, in which the adjuvants such as foaming agents in particular, are drawn in by suction in a metered manner and are fed to a suction pipe of an extinguishing fluid pump.
2. Description of the Prior Art
Methods and devices are already known for the automatic production of extinguishing fluids mixed with additives, e.g. foams, bonding agents, "Halon" or tear gas. For example it is known for the production of extinguishing fluids in expanded form, to install a by-pass pipe between a delivery pipe and an intake pipe of the extinguishing fluid pump. An admixing device for the foaming agents, advantageously being an injector admixing device, in which the negative pressure is generated by the extinguishing fluid flowing through the same, is situated in this by-pass pipe. The negative pressure generated whilst the extinguishing fluid flows through the admixing device is utilised to draw foaming agent from a foaming agent tank. The quantity of the foaming agent added in the admixing device is determined in the course of tests by means of a manually adjustable foaming agent restrictor element. Once the required consistency of the extinguishing fluid in foam form is reached, the adjustment is retained. It is disadvantageous in this solution that foaming agent is also drawn from the foaming agent tank even if no extinguishing fluid is delivered at the outlets of the delivery pipe.
In view of the pressure differential between the delivery and intake pipes, the extinguishing fluid actually flows through the by-pass pipe irrespective of whether extinguishing fluid is needed or not, so that foaming agent is constantly added to the extinguishing fluid contained in the by-pass pipe or in the extinguishing fluid pump. This frequently has the result of causing an accumulation of foaming agent in the delivery pipe, which is propagated in the direction of the foaming agent tank, so that the extremely undesirable mixing of the water commonly carried along in extinguishing fluid tanks with foaming agent must be prevented by installing a check valve in the intake pipe of the extinguishing fluid pump. This check valve is commonly formed by a flow flap which, in the case of back pressure of the foaming agent, blocks the displacement of the extinguishing fluid against the delivery direction, i.e. in the direction of the extinguishing fluid tank. Upon utilising extinguishing systems of this nature on mobile service vehicles such as fire fighting vehicles, this establishes the disadvantage that after an interruption of the extinguishing operation and a subsequent additional utilisation of the extinguishing fluid during a particular period, extinguishing fluid is present in expanded form in the delivery portion of the delivery pipes which lacks the desirable mixture of water and foaming agent.
Furthermore, it is also already known that foaming agent may be fed direct into the delivery pipe via a foaming pump separate from the extinguishing fluid pump, in particular after the high-pressure stage of the extinguishing fluid pump. The incorporation of a foaming pump in the high-pressure section however requires a comparatively great technological and financial investment.